package priv.pront.code.mati.province;

import java.util.Scanner;

/**
 * @Description:
 * @Author: pront
 * @Time:2023-11-17 10:15
 */
public class MC0205_找鸭子 {

    static String s;
    static char ans = 'A';
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        s = scanner.next();
        for (int i = 0; i < s.length(); i++) {
            char cur = s.charAt(i);
            if(cur > ans){
                ans = cur;
            }
        }
        System.out.println(ans);
    }
}
